The feeding biology of a species-rich genus of rainforest grasshoppers (Rhachicreagra: Orthoptera, Acrididae) : I. Foodplant use and foodplant acceptance.

1. 11 Costa Rican species of the forest light-gap grasshopper genus Rhachicreagra were shown by direct observation and by faecal analysis to be each narrow-range disjunct oligophages, eating typically only 3-6 species from the hundreds present in their habitat. The diet of the different species varies considerably, some pairs showing no overlap, others having several species in common. 2. All Rhachicreagra spp. accepted in captivity any plant found in the diet of any other congeneric species, but refused almost all other plants. There is thus a generic spectrum of acceptable plants. It includes one to several members of each of 7 families: Compositae, Urticaceae, Umbellifereae, Amaranthaceae, Phytolaccaceae, Gramineae and an unidentified monocotyledenous family. Within this range, the diet of any given species or population appears to be determined primarily by availability within the habitat. There is no evidence for the hypothesis that food-plant shifts are directly associated with speciation within the genus. 3. Compositae are a component of the diet of most species, and include the principal (=most used) foodplant of many, including the morphologically most primitive species. In lowland habitats, Urticaceae supplement or replace the Compositae in the diet, in montane habitats Hydrocotyle (Umbelliferae) is important. Phytolacca and Iresine (Amaranth.) are usually minor constituents of the diet of lowland species, but Iresine is the principal foodplant of Rh. obsidian. The monocotyledenous families appear to be eaten only when other footplants are in short supply. The literature suggests that the dicotyledenous families favoured are listinguished by their relatively high content of nitrogen and cations. They are also variously rich in saponins, flavonoids, alkaloids, polyacetylenes and sesquiterpene lactones. 4. The present ecological distribution of the genus is wider han that of any single known foodplant, and appears to be made possible by the diversity of the plants accepted; these include species typical of lowland and montane habitats and of drier and wetter climates.